Recently, an organic EL module that includes a built-in organic EL panel has drew attention as a lighting device that takes the place of an incandescent lamp and a fluorescent lamp.
The organic EL panel generally includes a base material such as a glass substrate and an organic EL element laminated on the base material, and has a structure for sealing the organic EL element and a structure for supplying power to the organic EL element.
The organic EL element includes two electrodes, one or both of which have translucency and which face each other and a light-emitting layer which is made of an organic compound and laminated between the two electrodes. The organic EL panel emits light by energy of recombination between an electrically excited electron and a positive hole.
The organic EL module uses a surface-emitting organic EL panel and is a planar light source. Thus, a plurality of organic EL modules may be laid on an installation target surface such as a ceiling so as to be used as a single lighting.
However, since the organic EL panel uses the energy of recombination between an electron and a positive hole as described above, the light-emitting amount varies according to the amount of current passing through the electrodes. That is, in an organic EL panel, since the internal resistance varies according to the quality of electrodes and a light-emitting layer, the amount of current passing through electrodes varies, and the light-emitting amount varies. Thus, there may be individual differences in quality among organic EL panels, even when the organic EL panels are manufactured in the same manufacturing line.
The influence on light emission caused by the individual differences in electric resistance value is small. However, when dimming control is performed on an organic EL module, precise dimming control cannot be performed. Further, when a plurality of organic EL modules are laid in a plane shape and used, lightness difference may be generated between adjacent organic EL modules.
In view of an actual condition of development, a product is improved from day to day. Thus, there may be a difference in manufacturing method depending on manufacturing time even among products of the same model or between a product of a current model and a product of a successor model. Thus, a slight individual difference may be generated between new and old products.
Thus, a conventional organic EL panel has a structure that is provided with a control board including a semi-fixed resistor to absorb individual differences between products. That is, an attempt to adjust an electric resistance value by a semi-fixed resistor to adjust the amount of power supplied to an organic EL element to prevent individual differences in the internal resistance between products as far as possible has been taken.
In a lighting apparatus using such an organic EL panel, it is desired to improve workability when electrically connected to an external device and reduce restriction in arrangement caused by the connection.
Thus, for example, Patent Document 2 discloses an lighting device including a light source unit and a mounting unit attached to a non-light-emission surface of the light source unit, the mounting unit including a circuit board for lighting-controlling of the light source unit and a connection terminal to which a conductor for electrically interconnecting the circuit board and an external device is connected. In the lighting device, the connection terminal is arranged inwardly from an outer peripheral end of a surface of the mounting unit to which the light source unit is attached, and a clearance is formed between the light source unit and the mounting unit in a state that the mounting unit is attached to the light source unit. In Patent Document 2, the lighting device enables a space for housing the conductor to be ensured between the light source unit and the mounting unit. Thus, even if an additional space is needed when the lighting device is electrically connected to the external device, for example, by bending the external conductor according to the arrangement, it is possible to ensure the additional space and to enhance the workability. In addition, in the lighting device, it is also possible to eliminate the restriction in arrangement for ensuring a space for housing the conductor.
Further, Patent Document 3 discloses a method for controlling power supplied to a light-emitting element. In this method, in order to reduce variations in light output based on individual differences between light-emitting modules as described above, a semiconductor memory that stores the characteristics of each light-emitting element is provided in each light-emitting module, and power supplied to each light-emitting element is controlled according to the characteristics of the light-emitting element read from the semiconductor memory.
Patent Document 3 also describes a lighting apparatus including a power supply terminal that supplies power to a light-emitting element and an output terminal connected to the power supply terminal through a resistor element, the lighting device feedback-controlling the power supplied to the light-emitting element on the basis of output of the output terminal. In the lighting device, a part of the resistor element is formed of a thin film-like resistor on a substrate having the light-emitting element and a resistance value of the resistor is adjusted by trimming to enable previous adjustment of the resistance value of the resistor element according to individual differences.